public class code {
    public static void main(String[] args) {
        double a = 0;
        double b = 0;
        for (int i = 1; i <= 100;i += 2){
            a += 1.0 / i;
            int j = 0;
            j = i;
            j++;
            b += 1.0 / j;
        }
        System.out.println(a - b);
    }
}
